A microcomputer-based instrument was developed to facilitate determination of the transepithelial resistance of an in vitro preparation of kidney tubule. The instrument controls the onset, intensity, and duration of a series of electric current pulses through the preparation, and measures the resulting voltages at each end of the tubule. Presently the instrument prints the currents and voltages from which the investigator must calculate the resistances and other parameters of interest. Plans call for enhancing the instrument to perform these calculations as well.